1. Field of the Invention
The present invention relates to a wavelength dispersive X-ray fluorescence spectrometer.
2. Description of Related Art
In the fluorescent X-ray analysis of a wavelength dispersive method, a sample is irradiated with primary X-rays, fluorescent X-rays emitted from the sample are then monochromated by a spectroscopic device and the monochromated fluorescent X-rays are subsequently detected by a detector (such as, for example, a scintillation counter or a gas flow proportional counter to generate pulses. The voltage of those pulses, that is, the pulse height depends on the energy of the fluorescent X-rays and the number of pulses per unit time depends on the intensity of the fluorescent X-rays. In view of this, by selecting pulses of a pulse height within a predetermined pulse height range from those pulses with the use of a pulse height analyzer, a counting rate thereof (the number of pulses per unit time) has been determined by a counting unit (a counting circuit) such as, for example, a scaler or the like.
When one pulse is generated upon incidence of X-ray photon on the detector, no pulse is generated for a defined period of time subsequent thereto, that is, a so-called dead time, even though X-ray photons are incident on the detector. Also, if the counting rate becomes high, pulses become overlapped within the counting unit. In view of those, a counting loss of the pulses to be counted tends to occur.
Accordingly, it is a conventional practice that as regards to both of the counting loss resulting from the detector and that in the counting unit, with respect to the specific pulse height range the dead time τ is determined for each detector as one value and, using this dead time τ, by means of, for example, the following equation (1), the counting rate (counting intensity) Nm of the pulses determined by the counting unit is corrected, followed by determination of a counting loss corrected counting rate, that is, a counting loss correction intensity Nt. In this respect, see, for example, the patent documents 1 and 2 listed below.Nt=Nm/(1−τNm)  (1)
Also, an equation in which the counting rate different from the equation (1) above is used so as to avoid effects brought about by higher order reflection lines of inter-elements (See, for example, the patent document 1 listed below.), an equation in which a denominator of the equation (1) above is rendered to be an equation of higher degree with respect to Nm, different values of coefficients are employed and the equation thereof converted into a table (See, for example, the patent document 2 listed below.) have been suggested. According to those equations and tables for the counting loss correction, which are employed in the conventional art, even though the predetermined pulse height range, within which pulses are selected by the pulse height analyzer, is changed depending on a measurement, the counting loss correction intensity is determined while the coefficients of Nmn remain the same regardless of the change of the predetermined pulse height range.